Tenerife
Mount Tenerife, located in the Magallanes region, has an unmistakable pyramid shape, identifiable from miles away, and is in fact on the way to Torres Del Paine National Park.
To enter and attempt its ascent you must go to the Torres Del Paine Complex, where you must go to one of the houses of the locals to request permission to enter, as well as to announce your departure. The locals are very friendly people.